(1) Field of the Invention
The present invention relates to a free-ink type writing instrument having an ink collector which temporarily stores ink flowing out when the pressure inside the ink tank increases.
(2) Description of the Prior Art
There have been known free-ink type writing instruments which use a temporary ink collector arranged radially outside, and separated from, its ink feed connected to the ink tank and made up of a molding having a comb-toothed section or an temporary ink collector made up of a porous structure and filled up with a water-based ink having a surface tension of greater than 30 mN/m under 25xc2x0 C. ambient temperature, whereby ink from the ink tank is temporarily held in the ink collector when the internal pressure of the ink tank space increases so as to prevent ink ejection from the writing point. In these writing instruments, the combed teeth are arranged with their gaps equal to or greater than 0.2 mm.
When, however, a line is drawn on the writing surface having a low surface energy such as polypropylene or polyethylene sheet, paper with sebum adhering thereon, glass surface, or the like using a water-based ink having a surface tension of greater than 30 mN/m, there is a problem of drawn lines being repellent (ink of drawn lines being unable to stay on the writing surface).
In order to solve this problem, ink should preferably have a surface tension of 30 mN/m or below and more preferably have a surface tension of 27 mN/m or below. Such ink of a low-surface tension is often used for oil-based makers and water-based makers having beneficial adhesiveness, but such writing instruments are not of free-ink type including a sectionally comb-shaped temporary ink collector.
Further, when an ink having a surface tension of 30 mN/m or below is charged to a free-ink type writing instrument having the aforementioned combed teeth gaps of 0.2 mm or greater, because of its low surface tension hence insufficiency of the capillarity of the gaps, most of ink having flown into and between combed teeth cannot stay therein but will leak out from the writing tip when the pen is put with its writing point downward. On the other hand, liquids of a large surface tension generally present a low vapor pressure so are poor in their drying property.
It is therefore an object of the present invention to provide a free-ink type writing instrument which is able to use an ink having a surface tension of 30 mN/m or lower so that lines of the ink can be drawn without being repellent on a writing surface of a low surface energy and the ink is excellent in drawn line drying property, and still can retain the whole ink that has been pushed out by volume expansion of the empty space inside the ink tank due to ambient changes, within a temporary ink collector without forward leakage of ink from the writing tip.
In order to achieve the above object, the present invention is configured as follows:
A free-ink type writing instrument according to the present invention includes: an ink tank chamber; a writing tip; a temporary ink collector having a sectionally combed configuration, disposed between the ink tank chamber and the writing tip; a partitioning wall having an air replacement hole therein, disposed for separating the ink tank chamber and the temporary ink collector; and an ink feed or pen core arranged so as to penetrate through the temporary ink collector and projected into, or penetrated up to, the ink tank chamber, and is characterized in that the sectionally comb-shaped temporary ink collector is disposed 2.0 cm or greater away from the writing point, all or part of the gaps between neighboring combed teeth for retaining ink in the temporary ink collector are set equal to 0.15 mm or smaller, and the ink tank is charged with an ink having a surface tension equal to 30 mN/m or lower at 25xc2x0 C.
In the present invention, not all the gaps between neighboring combed teeth should be necessarily set equal to or smaller than 0.15 mm(preferably 0.13 mm), but it is more preferred that at least part or all of the combed gaps located 2.0 cm or greater away from the writing point should be set equal to or smaller than 0.15 mm(preferably 0.13 mm). Also in the portion near the writing tip or located less than 2.0 cm away from the writing point, it is preferred that the combed gaps are set equal to 0.15 mm or smaller (preferably 0.13 mm), in view of securing a greater capillarity. However, since the stored amount of ink per tooth becomes low, such setting is inefficient in view of material consumption. Therefore, the combed gaps located less than 2.0 cm away from the writing point should be determined as appropriate considering the ink""s surface tension., economical efficiency, global environment concerns and the like.
Concerning the organic solvents used as the solvent for ink, any organic solvent can be used as long it is generally used for writing instruments. For example, monohydric alcohols such as ethanol, n-propanol, etc., polyhydric alcohols such as propylene glycol mono-methyl-ether, etc., can be considered.
Any material can be used for the ink tank chamber and the sectionally comb-shaped temporary ink collector as long as it does not cause swelling, whitening, dissolution, embrittlement and other defects when it is put into contact with ink. When considering moldability, economical efficiency, global environment concerns such as recylability, a resin selected from a group made up of polyester resin, polypropylene resin, polyethylene resin, polyamide resin is preferably employed as the material for the ink tank chamber when an organic polar solvent is used as the main solvent of the ink; a resin selected from a group made up of polyethylene resin, polyamide resin is preferably employed when an organic non-polar solvent is used as the main solvent. When water is used as the main solvent, a resin selected from a group made up of acrylic resin, styrene resin, vinyl polymer, vinylidene polymer, polycarbonate resin, polyester resin, polyolefine resin such as polypropylene, polyethylene, polyarylate resin is preferably used. As the material for the sectionally comb-shaped temporary ink collector, a resin selected from a group made up of polyester resin and polyolefine resin such as polypropylene, polyethylene is preferably used when the organic solvent is of a polar solvent; a resin selected from a group made up of polyethylene resin and polyamide resin is preferably used when the organic solvent is of a non-polar solvent; and acrylic resin, polystyrene resin, vinyl polymer, vinylidene polymer, polycarbonate resin, polyester resin, polyolefine resin such as polypropylene and polyethylene, polyarylate resin, ABS resin, polyacetal resin and others can be preferably used when the ink is based on water as the main solvent.